Composite friction bearings or laminate materials for the production of composite friction bearings can be considered as laminate materials or laminate workpieces of a type in which the friction bearing layer representing the functional layer comprises a dispersion alloy, in particular lead-bronze or an aluminum/tin dispersion alloy or an aluminum/lead dispersion alloy, and is applied to a backing layer, primarily of steel, which forms a bearing shell. Composite bearings of laminate material of the steel/lead-bronze type are of particular significance because of their high dynamic load-carrying capacity and the good run-in and emergency-running properties of the lead bronze. Due to the total insolubility of the two metals in each other in the solid state, there is practically a mechanical mixture of copper and lead in the present functional layer consisting of lead bronze, that mixture being produced from the homogeneous molten material in the course of a long setting period. The steel/lead-bronze laminate materials which are conventionally used nowadays and which are produced by a strip coating process on steel are restricted to lead contents of up to about 22% by weight of the lead bronze. The difficulties in regard to manufacture of copper/lead alloys with lead contents within the miscibility gap, that is to say lead contents of between 40 to 50%, are so great that hitherto such alloys have not been of any practical significance. The bond between the steel backing member and the cast layer of lead bronze thereon is a strong metal bond between the steel backing member and the copper crystallites which are formed primarily by solidification from the molten material. Therefore, the formation of such copper crystallites must be utilized in the interest of achieving a good bond between the steel backing member and the lead bronze layer. In practice, that is achieved by an operation which provides that, for casting the lead/bronze thereon, the steel is raised to and held at a temperature of about 1100.degree. C., which permits diffusion bonding between the steel and the copper crystallites. On the other hand, the structure of the lead-bronze functional layer, which is heterogeneous due to the copper crystallites and the lead precipitates, gives rise to serious functional disadvantages in comparison with a homogeneous functional layer structure. Comparable circumstances also arise in regard to friction bearing layers which represent the functional layer, consisting of aluminum/tin dispersion allows and aluminum/lead dispersion alloys, as well as all conceivable functional layers for tribological purposes with a heterogeneous structure, for example mixtures which are fixedly combined in themselves and which are substantially fusible, made of components which are not soluble in each other or which are soluble only in an amount which is smaller than the amount present.
German Open Application 29 37 108 already discloses a process for refining sliding alloys, in particular sliding or friction bearing alloys, in which the alloy is to be subjected to a local punctiform melting effect by one or more highly concentrated energy or heat beams, wherein due to the progressive movement of the punctiform surface portion which is subjected to the energy or heat beam and due to the dissipation of heat which occurs in the material of the functional layer, that process causes sudden cooling of the molten material. In that known process, however, the functional layer which is of a heterogeneous material structure is melted in the punctiform areas over its entire thickness, that is to say, as far as the region of bonding thereof to the backing layer. However, the amount of heat which is supplied in that operation is so great that the intended sudden cooling effect is so slow--not least because of the latent heat of fusion which is released again when the material resolidifies--that the reformation of a heterogeneous structure in the functional layer is inevitable. That procedure provides at best for a more or less slight refinement effect in comparison with the original structure. It is not possible in that way, to achieve a substantial improvement in the functional properties of friction bearing layers made of dispersion alloys and other mixtures which can be used for tribological purposes. In the case of functional layers of lead bronze, the desired diffusion bonding effect is eliminated or at least made substantially worse due to the fact that the functional layer is locally melted over its entire thickness.
It is known from EP 130 175 A2 and 130 176 A2, in relation to friction bearings, to form areas of different levels of hardness in the running surface, by a process which provides that hardening material components are fused into the surface region of the running surface, in delimited zones of the running surface, preferably utilizing laser beams or electron beams. That provides a bearing running surface in which the bearing layer has areas with different levels of hardness, but it does not provide a surface refinement effect which extends over the entire running surface, in the sense of improving the functional properties and, in particular, the tribological properties to the same degree at all parts and areas of the surface of the functional layer.
Finally, it is known from German Open Application 36 36 641 and EP 212 938 A2 to form sliding or friction bearing layers on a strip-like carrier, for example a steel backing member, by a procedure which provides that a mixture of the alloying components is first applied in a powder form to the backing member. The powder is then progressively locally melted, using an energy beam, namely, a laser beam, which is guided over the layer of powder in a predetermined pattern. Admittedly, it is possible for the layers produced in that way from a dispersion alloy to have a finer structure than that found in cast functional layers made from a dispersion alloy. However, it is also not possible in that way to produce functional properties which are comparable to a finely divided structure which is close to a homogeneous structure in respect of the functional layer. In addition, the fact that previously sprinkled powder is caused to melt progressively in a punctiform area means that the desired diffusion bonding effect between the backing layer and the functional layer cannot be attained.